LED-based light systems are used to produce white light for applications such as liquid crystal display (LCD) backlighting. One technique for producing white light involves mixing the light from red, green, and blue (RGB) LEDs. White light generated from an RGB LED-based light system tends to be inconsistent in quality, especially as the LEDs degrade over time. Feedback control systems have been used to measure luminance and chrominance characteristics of the output light such as the brightness and color point and to adjust the LED drive signals to maintain the desired luminance and chrominance characteristics of the emitted white light. As time goes by, degradation of the individual LEDs in an LED-based light system causes changes in the brightness and shifts in the color point of the emitted white light. The feedback control system adjusts the drive signals to compensate for the changes in LED performance. Typically, as an LED-based light system degrades, the LEDs must be driven harder (e.g., with a higher drive voltage or drive current) to maintain the brightness of the red, green, and/or blue LEDs. Driving the LEDs harder causes the LEDs to dissipate more heat which further degrades LED performance.
At a certain point, the feedback control system will not be able to maintain the desired brightness and color point of the emitted white light due to the degradation of one or more of the LEDs. Although the LED-based light system is still able to produce white light, the light no longer has the desired luminance and chrominance characteristics and the LED-based light system must be replaced or the inferior quality of light accepted.
In view of this, what is needed is an LED-based light system that can produce light of a desired quality for longer than current LED-based light systems.